In modern motor vehicles, in the foreseeable future at least two different vehicle electrical systems are coming into use, for example a 12V vehicle electrical system and a 48V vehicle electrical system, which supply different electrical/electronic loads of the motor vehicle with the electrical supply voltage which is required by them. In order to conserve the energy supply units of the motor vehicle—usually rechargeable batteries—when the motor vehicle is in a parked state, and consequently can not be recharged during driving operation by means of a generator, installed in the motor vehicle, the electrical loads present in the motor vehicle can be switched between an active state and a so-called idle state. In other words, the electrical loads are able to separate themselves electrically from the respective vehicle electrical system by means of an electrical/electronic switch or by the use of suitable integrated circuits (ICs) in the manner of voltage converters, communication ICs, etc., or are able to at least shift into a state of greatly reduced current drain. Said idle state is therefore distinguished by a greatly reduced electrical energy consumption of the respective electrical load. In particular, in this way an undesired complete discharging of the energy supply units is prevented, when the motor vehicle is in parked state.
In contrast, in the active state the electrical loads are connected to at least one vehicle electrical system. Consequently, at least one vehicle electrical system can provide the electrical load with electrical energy. In order to switch the electrical load from the idle state into the active state, which corresponds to a so-called “wake-up”—therefore a “waking up”—from the idle state, an electrical/electronic switch, which separates the electrical load from the vehicle electrical system, is switched into a closed state, so that the electrical load is electrically connected, for the supply of energy, to the vehicle electrical system. Such a switch is typically part of a vehicle electrical system part of the electrical load, via which the load draws electrical energy from a particular vehicle electrical system. For each vehicle electrical system, from which the electrical load is to draw electrical energy, an individual vehicle electrical system part can be provided.
For the case where the motor vehicle has several loads, such a wakeup signal must be conveyed individually to vehicle electrical system parts, and each vehicle electrical system part must be switched separately from the idle state into the active state. A corresponding activation signal can be provided to the electrical load of the motor vehicle for example by a CAN- or LIN bus system present in the motor vehicle. However, such a bus system is generally only associated with a particular vehicle electrical system or respectively is referenced to its voltage level.
It proves to be problematic here to pass this wakeup signal on to all further vehicle electrical system parts of the electrical load, if for example galvanically separated or at least low leakage current interfaces are used here between the vehicle electrical system parts, which would already have to be supplied with electrical energy for the function, i.e. would already have to be “woken up”, therefore activated, before the actual wake-up.